Variable loss paramagnetic cores



May 20, 1952 A. w. FRIEND 2,597,237

VARIABLE LOSS PARAMAGNETIC `CORES Filed June 25, 1948 INVENTO R ATTORNEY Patented May 20, 1952 UNITED STATES PATENT OFFICE VARIABLE LOSS PARAMAGNETIC CORES Albert W. Friend, Lawrenceville, N. J., assignor to Radio Corporation of America, a corpora tion of Delaware Application June 25, 1948, Serial No. 35,177

7 Claims.

This invention relates to paramagnetic cores for electrical inductances and the like, and particularly to a novel method of treating paramagnetic cores to provide a core having nonuniform losses and .to variable loss cores obtained by such method.

`Paramagnetic cores which have non-uniform f or progressively increasing losses along a predetermined direction anda substantially constant magnetic permeability may find Wide application. Thus, such `cores might be used in tuning inductances to vary the Q of a resonant circuit Without changing the resonant frequency thereof. The Q of a circuit is dened as the energy stored by the circuit divided by the energy dissipated per cycle of the resonant frequency of the circuit. Expressed mathematically: i

wL 21rfL Where f is the resonant frequency of the circuit,

L its inductance and R its resistance. The pass band of "a circuit is dependent on the Q. Thus, when Q is larger than 3, the following relation holds:

Y Q fzf1 Where f2 is larger than i which is larger thanfi. f2 and fr are the frequencies where the response of the circuit which is unity for f, has been reduced to Accordingly, the band of the circuit is:

. in the deflection'yoke. of the deflection, circuit for a television picture reproducing tube in order to adjustrthe damping of the circuit and thereby the linearity of the beam trace.

I A broadcast receiver conventionally includes a signal frequency circuit whose resonant frequency is tunable within a predetermined frequency range. It may be desired to maintain constant the band Width of the modulated wave passed by the signal frequency circuit in which case the Q of the circuit must vary with the frequency. It is conventional practice to tune the signal frequency circuit of a radio receiver by moving a paramagnetic core with respect to the coil'of the resonant circuit. This Will vary the inductancev of the coil and thereby the resonant frequency of the circuit. In such a case, a variable loss core, that is, a core having non-uniform or progressively increasing losses can be used with advantage because the Q of the circuit tube can be varied inversely with the frequency to maintain the band width constant over a wide frequency range.

It is accordingly the principal object of the present invention to provide a method of producing avariable loss paramagnetic core and a variable loss core manufactured in accordance with the method. Y Y

A further object of the invention is to provide a paramagnetic` core having a continuously increasing loss along a predetermined direction and a substantially constant permeability.

Another object of the invention is to provide a variable loss paramagnetic core for a resonant circuit to adjust the Q of the circuit by varying the relative position of theV core with respect to the coil of the circuit Without materially changing the inductance of the circuit.

In accordance with the present invention, there is provided a core consisting of comminuted paramagnetic particles electrically connected to each other by semi-conductive paths, the number of the paths varying in a predetermined manner along a predetermined direction such as the axisfof the core. Thus, a change in the loss of the core is effected along the core axis. Such a core may consist of comminuted paramagnetic particles bonded together by a, carbonaceous binder such as a resinous binder. The core may beV manufactured by subjecting it to heat treatment which varies in such a manner that the binder becomes carbonized to an extent which changes alonga predetermined direction of the core. It is feasible to vary the temperature to which the core is subjected along the core axis, or alternatively, the temperature may Ybe maintained constant but the core may be subjected to the heat treatment for a time duration which varies along the axis. I Y

small amoun t,-of carbonaceousbinder. binder may consist Of-any organic material which ,..dldefp -binder'arepressdinto the desired shape under The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects 4and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing, in which:

Fig. 1 is an elevational view of a paramagnetic core being subjected to ahigh frequency-field;

Fig. 2 is an elevational view of a paramagnetic core surrounded by a variable pitch coil energized by a high frequency generator;

Fig. 3 is an elevational view, partly in seotion, of a paramagnetic core being subjected to a temperature varying along its axis;

Fig. 4 is an elevational View, partly in section, of a paramagnetic core being subjected to a variable heat treatment;

Fig. v5 isu a 'schematic view of a variable loss core Yi'n "accordance with the present invention vwvhichisutilied for varying the Q of a resonant ciruitend Figfis'an.elevational View, partly in section,

. of a variable'loss coreembodying'th'e present invention and uarranged'in a shunting frame from acoil.

Referming now'to Fig. l, there is illustrated Hparamagnetic" core I0 which may be composed -of powde red OrcOmminuted iron or other nely divided pararnagnetic or ferromagnetic materials.

jA pararnagnetic material yis del-ined as a material lhaving a rnagneticrpermeability greater than that of a vacuum, which is unity. Theimagnetic permeability of a paraniagnetic material may be indep endent jo f jt he'magnetizing force,'or it may vary.with the magnetizing'forca in which case the. materielle Called ferrelglietia A- high permeability core may be obtained in K the following manner. Low cost sponge iron/and electrolyticjiron powders are 'mixed with'a very o. The

, .This fiortalrip'laarssin binder isi Suitable and particularly eresie bld'sf @f 'fh'ihnol formal- -Theferromagnetic powder and the A veryfhifgh molding pressures. A moldingpressure of between v1 5fafn k l-`60 tons `rper Vsquare'inch has been usedto I "ecl'iieV the inter-particle insulation furnishedbyV thebinder to a minimum thickness so'that-nornially eddy currents can not flow in more than one particle of the ferromagnetic ma- In order toobtainthe best electrical, magnetic ,and-mechanical properties the optimum amount One'of the resins 'was aliquid resin containing 'about "9o-per cent "solids -while the other Was a nely divided solid resin. A core of this type may Vhavea high permeabilityof the order of perhaps 50'to 250.H Theicoreimay then be cured, that is," Athe core'is heated to set the binder, which is usuallyfcalled thermo-setting. 'This method of manufacturing a pararnagneticV core j is conventional "and has been -set forth, for example, inf

the copending application to Friend and IrIaroling,`- Serial No. 781,804, filed on October 24, 1947 and 75 form loss of the present invention. In this case,

4 entitled Comminuted Ferromagnetic Cores (RCA-10,697)

A heat treatment which permits a uniform increase of the loss of the entire core whereby the finished core has a uniform high loss has also been described in thecopending application to Friend vand Harding referred to. 1 The purpose of this heat treatment is to convert the binder partially or totally to nely divided carbon. Thus, after the core has been cured, it may then be subjected to a temperature between approximately 800,a to 1000 F. When the core is heated to 10009,',it may be'subjected to this temperature fora durationof no more than about 20 minutes. On the other hand, when the core is heated to 860 only, it'may be subjected to this temperature for a duration of perhaps minutes. However, the length of time during which the temperature is applied is a function ofthe penetration ofthe heatinto the core. fWhen 'ajcore is heat treated in this manner the carbonac'eous binder of the core is suiciently carbonized to provide a'number of semi-conductive'p'athsibetween the ferromagnetic particles to obtain a high loss core.`

If the core is'heatedito ajsumcientlyihighftemperature some of the ferromagnetic particlesmay be sintered together soastoconnecttheinelectrically, The Veffect of the 'heat treatment, fjaccordingly is ft'o increase the conductive paths betweenthe ferromagnetic particlesiintwoways.

.the iron. particlesi creases the'lsses,fther"e is undoubtedly a modification of the magnetic properties ofthe surfacevlayers vofthe particles.A In accordance with the present inventionfcore I0 is subjected to such anheat treatment that the losses of the core will increase progressively along a predetermined direction such as the longitudinal axis of V,the 'c ore;V Acordingly, core IIlfw'hich ,has been molded and curedin the..'.m'a' r`1erf explained herein, may then be heattratedby a high frequency electromagnetic field. Tomthis end, there is provided high frequency generator II which is connected tocoil I2 whose length is small compared. to that of core I0. Core III is moved'relatively to'coil I2 as illustratedbyarrow I 3 at a non-uniform speed. The electromagnetic field developed by `coil'I2 will heat core I0 to theY desired. temperaturevvhich Ywillbe substantially uniformj in the portion 'of` coil" II) arranged'withi'ri c'oilIZ. ,A Bymovi'ng'itheicre'at a non-uniformspeed Iwith respe'cti to coil; |10 k,the duration or the heat; treatment jriiayA be varied along the core ,axis fandtlie',isulting'fcore `will have a loss varying 'continuouslyalngits axis. The permeability' ofthe core memainsfsubstantially constant, unless'excessive h'eat islapplied. Generator .I Iv "mayv developA a freduncyingthe neighborhood, of l0 m'e'gacycles.A ,It is' t'offlef nderstood, however, that frequencies 'fas low as 10,000 cycles or less couldbeused.

high frequency generator Il is connected to coil I5 which has a variable pitch, as illustrated. During the heat treatment, core I remains iixed with respect to coil l but the mean strength of the electromagnetic eld will diier along the axis of core lll.v Accordingly, the temperature will differ along the core and the losses of the finished core I0 will increase continuously along the axis of the core, the variation of the loss being determined by the pitch of coil l5.

A further arrangement for practicing the invention is shown in Fig. 3, in which core I0 is heated by means of flames shown schematically at I6. It is to be understood, however, that it is preferred to effect the heat treatment by a high frequency electromagnetic eld in the manner explained in connection with Figs. l and 2. As illustrated in Fig. 3, core I0 is arranged in cylinder I1 which preferably consists of a heat conducting metal. The flames heat end plate I8 fixed to cylinder l1. The open end of cylinder I1 may be secured to cooling plate 20. The temperature gradient along cylinder l1 caused by heating end plate i8 by iiames I6 Vwill vary the temperature along the axis of core I0. The resulting core again has a variable loss along its axis.

Fig. 4 illustrates a modiiied method of heating core I by means of iiames I6. Core l0 rests in a cylinder 22 of a heat conducting material such as a metal. Flames I5 are spaced in the manner illustrated so that the left hand portion of core ID will be heated to a higher temperature than the right hand portion. Accordingly, the finished core will have higher losses at its left hand portion than at its right hand portion. If desired, to provide a very uniform product, cylinder 22 mail be rotated during the heat treatment so that the temperature of each cross-sectional area will be substantially uniform.

It will accordingly be seen that core I0 may be heated in any suitable manner such as by an electromagnetic i'leld or by the application of a iame. When core l0 is heated by a high frequency electromagnetic field, the heat penetrates uniformly through the entire thickness of the core. Accordingly, in that case, the duration of the heat treatment can be shorter than when the core is heated by the external application of the heat. The heat treatment is such that either the temperature changes along the core or that a xed temperature is applied for a variable time duration to diiferent portions of the core. It is to be understood that core l0 could be molded into any desired shape such as a cylinder or a rod having a square or a rectangular cross section. Alternatively, the core could be molded in toroidal shape.

A variable loss paramagnetic core manufactured as described herein may ind wide application. As illustrated, for example, in Fig. 5, variable loss paramagnetic core 25 may extend through inductance element 26 which may be resonated by capacitor 21. By moving core 25 in the direction of arrows 28, the loss of resonant circuit 26, 21 may be adjusted. Thus, resonant circuit 2B, 21 may be the output or input circuit of an intermediate frequency amplier in a superheterodyne receiver. By moving core 25 in the direction of arrows 28 the Q of the resonant circuit may be adjusted and accordingly the band width of the circuit. It is assumed, of course, that the magnetic return path remains essentially xed when core 25 is adjusted. This may be achieved by utilizing a core 25 which is long compared to coil 26.

It is also feasible to maintain the magnetic return path fixed in the manner illustrated in Fig. 6. In that case, paramagnetic c ore 25 is arranged in shunting frame 30, 3l which houses coil 32. Shunting frame 30, 3l may consist of two portions as disclosed and claimed in the copending application to Friend Serial No. 619,870, led on October 2, 1945, now Patent No. 2,513,160, dated June 2'1, 1950 and entitled Transformer (RCA 24,237) It is, however, also feasible to use a one part shunting frame although a shunting frame consisting of two parts such as 30, 3l' reduces the effective reluctance of the air gap. The Q of coil 32 may be adjusted by moving core 25 in the direction of arrows 28 so that a higher or lower loss portion is arranged in coil 32. shunting frame 30, 3l provides a magnetic return path of fixed reluctance and loss properties for core 25 and coil 32.

It is to be understood that the variable loss core of the present invention may also be used for other purposes such as to vary the attenuation of a circuit. It is also feasible to utilize a core in accordance with the invention for tuning a resonant circuit and for varying its Q inversely with variations of the resonant frequency of the `circuit. This'may be done in the signal frequency input circuit of a broadcast receiver. The variable loss core of the present invention may further be used for adjusting the damping in the output transformer or deection yoke of the deflection circuits of a television receiver. By adjusting the damping of the circuit the linearity of the trace on the target of the picture reproducing tube may be controlled. Other applications of the core of the invention will readily suggest themselves.

There has thus been described a method of manufacturing a variable loss paramagnetic core and a core produced in accordance with the novel process. The core has a loss which varies or changes continuously along its axis.

What is claimed is: l

1. A ferromagnetic core for tuning inductances and the like, comprising a body of ferromagnetic particles and a carbonaceous binder having electrically conducting carbonized particles included therein in increasing concentration per unit of volume along a predetermined direction through the core, and having a resultant eddy current loss increasing along said predetermined direction and a permeability which is substantially constant along said direction.

2. A core for an inductance device consisting of comminuted and sintered paramagnetic particles electrically connected to each other, and means therebetween providing electrical semi-conductive paths, said means comprising carbonized particles of carbonaceous binder material varying in concentration per unit of volume along a predetermined direction of said core to effect a variation in the loss of said core along said direction.

3. An electrical inductance core consisting of a mixture of comminuted ferromagnetic particles, electrically non-conducting carbonaceous binder material, and finely divided carbonized particles of said material in varying concentration per unit of volume along a predetermined direction of said core, said last named particles being at least semi-conducting electrically, thereby to effect a variation in the loss of said core along said direction without substantially aiecting the permeability of said core.

4. An electrical inductance core consisting of a mixture of comminuted ferromagnetic particles, resinous binder material, and finely divided carbonized partiel@ Qf-'Saiflrmatgrial varjynsin .conf cetration pei f '7" ntiniiogly yalong` a,y'predetermined direction of said core, s'i'idflast named"y particles` beingl electriolly conducting thereby' to effect ajoiiiiiiu'ous; vriatiqii in, the loSsv Of fsaidlcore along sici'directioi,Without$1110L stantially changing tl permeability ofjsaid'co're.

5. A creior an electricl-inductafnceiconsist inglof` abody'of coinniiriuted ferromagnetic prir-4 ticles Aand a c`arbownfa'fzeoli's inferiaflfas aiv binder therefor,` said material 'being'y carl/oonized vand elerically condu'ctingftofanextent Varyii'igin a predetermined Irnannij'along' predetermined direction of Said cijr'eandfsorrie of sid ffe1f1'o-ni1lg.-vv netic particles being 'in Sinteijd'electrical contact with each other, th nriiberof sid contoting particles' varying iii" 'concentration' 'per niij pf volume ,along thev core in said direction, thereby to 'iect a Variation the'loss'of-Sid,oiealong said directionv without substantially aiiciiii'g the permeability of Said core.'

6; A`core'forfelectricalfinductance deviceg and the like, CQnSistingf,pmminutederomagneic particlesnd' a, lcan#kioi12ice1`1s` binder, vSaid, 1921'- ticl'es being 'irl sinteijed Contact l,and of increasing size 'along' a predetermined'dirction lof' said core, thereby effectV vairiationin the yeddy current REFERENCES CITED#Y Tiiel following references are ofreqordjrnthe lepfvthis. patenti.

UNITED STATES -PATEN'PS 

1. A FERROMAGNETIC CORE FOR TUNING INDUCTANCES AND THE LIKE, COMPRISING A BODY OF FERROMAGNETIC PARTICLES AND A CARBONACEOUS BINDER HAVING ELECTRICALLY CONDUCTING CARBONIZED PARTICLES INCLUDED THEREIN IN INCREASING CONCENTRATION PER UNIT OF VOLUME ALONG A PREDETERMINED DIRECTION THROUGH 